Effect of Emulsifier Concentration on the Oxidation of an O/W Emulsion Prepared from Canola Oil

In most cases, oils and fats are present as emulsions, such as water-in-oil (W/O) emulsion (e.g. margarine and butter) or oil-in-water (O/W) emulsion (e.g. beverages, milk, and fresh cream). Some studies have shown that oxidative deterioration of foods containing oils and fats may be affected by light, temperature, metals, or peroxide contained in food. In fact, oxidative deterioration is a large economic concern in the food and preventing the oxidation of emulsion is of vital importance for the food industry.

In this study, the effect of different concentrations of Tween 20 (0.5, 2.5, 5.0, 10 w% vs. oil) on the oxidation of canola oil O/W emulsion was investigated. Oxidation was conducted at 34°C in the dark and accelerated using 2,2-azobis (2,4-dimethylvaleronitrile) (AMVN) and 2,2’-azobis (2-methylpropionamidine) dihydrochloride (AAPH) as radical generators. Peroxide value (PV, mEq/kg) was monitored as generation of the primary oxidation compound. Tocopherol content of oil was analyzed by high performance liquid chromatography (HPLC). Particle size of emulsion was measured using an inverted optical microscope (200x), and calculated with “Image J” software (National Institute of Mental Health, Bethesda, MA).  

The results showed that PV was suppressed by Tween 20 in a dose-dependent manner in both emulsion system using AMVN and AAPH, and the tendency of suppression was clearer in the system using AMVN than in that using AAPH. Contrarily, there were no significant differences in PV when emulsions were prepared with tocopherol-stripped oil. The particle size of emulsion droplets were also consistent among emulsions prepared. However, tocopherol contents at lipid phase of the emulsions prior to oxidation decreased with concentration of Tween 20.

In conclusion, although the effect was modest, excess amount of Tween 20 modified the antioxidant efficacy of tocopherol in a dose-dependent manner. The speculation is that Tween 20 can help tocopherol to migrate from the lipid phase to the oil-water interphase, where the oxidation occurs. Further research to define the optimum combination of oil, water, and emulsifier is required.

Article by Yukihiro Yamamoto and Rino Misawa, from Prefectural University of Hiroshima, Shobara, Japan.

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Image by Indirect Heat, from Flickr-cc.